Boone, Mollusca, Cruises of "Eagle" and "Ara," 1921-28 179 



to a triangle on either side of the siphon, being concave between 

 these angles. The head is of moderate size, decidedly flattened dor- 

 sally in all nine dead specimens before me, the length in the median 

 line one-third less than the greatest width, which occurs in the ocular 

 region. The eye is large, pupil circular. The ventral surface of the 

 head is excavate for the reception of the dorsal side of the siphon. 

 The siphon is large, stout, with a bilabial aperture. The outer buccal 

 membrane is large, produced into seven acute angles. The buccal 

 process is capable of being produced almost entirely beyond the head. 

 The beaks of the jaws are both strong. The female has no espe- 

 cial tubercle for the attachment of spermatophores. All the arms 

 are short, successively increasing in length by 3 to 5 mm. each, in the 

 order 1, 2, 3, 4 (fig. A). The dorsal arms have a strong median 

 dorsal carina extending their entire length ; the second pair are thick 

 at the base and keeled on the lower outer margin ; the third arms are 

 heavily keeled throughout their entire length but especially so on the 

 distal half; the fourth arms, which are only a little longer than the 

 third pair and have a wide membrane on the upper angle which 

 expands at the base and connects them with the third pair, a narrower 

 membrane runs along the ventral margins. The suckers of the sessile 

 arms are in two rows, extending quite to the tip of the arm. The 

 suckers are small, cup-shaped, very deep and oblique, the sinus much 

 higher on the outer side, where the chitinous rim is divided into 

 several wide, bluntly rounded teeth, distinctly separated by narrow 

 spaces. On the smaller, more crowded cups towards the distal tip 

 of the six arms, these teeth are usually more acuminate. 



In the dead specimens the tentacular arms are as long as the body ; 

 it is very probable that in the living ones they are even longer. At 

 the base these arms are stout, farther out, compressed, the club very 

 well developed, approximately twice as wide as the rest of the arm, 

 with a thin, elevated, oblique dorsal keel arising midway the club 

 and extending to the tip. The suckers are arranged regularly in four 

 rows, 8 to 10, occasionally 12 large suckers in each row, followed 

 distally by a series of smaller suckers, which in turn are succeeded by 

 the even smaller, smooth-rimmed terminal suckers. The larger suckers 

 of the median rows are slightly larger than those of the adjacent 

 lateral rows, and are wide, cup-shaped, the rims cut into sharp, 

 incurved teeth smaller on the inner side; the suckers of the lateral 

 rows are comparatively large, deep, cup-shaped, very oblique with 

 the outer half of the horny ring cut into acute incurved teeth. The 



